There are critical knowledge gaps regarding the risk of Listeria monocytogenes in raw agricultural commodities (i.e., intact whole fruit and vegetable commodities that are not cut or processed). This is of particular concern as outbreaks have occurred from intact whole produce commodities, such as cantaloupe and stone-fruit. Since it is widely accepted that L. monocytogenes may be present in produce production environments, data on L. monocytogenes behavior on whole produce, after harvest, when handled/stored at typical and abuse conditions over typical shelf life (and beyond) are needed. This project will determine L. monocytogenes growth and survival potential on intact whole produce commodities and develop quantitative risk models for selected commodities that demonstrate growth or significant survival potential. These goals will be achieved using a three-pronged approach of i) investigating prior information (systematic literature review), ii) filling critical data gaps (L. monocytogenes growth/survival experiments), and iii) developing risk models to assist the industry in managing the risk from L. monocytogenes contamination. Knowledge on which whole produce commodities support L. monocytogenes growth and/or survival potential at various handling and storing conditions observed along the supply chain will be created.

Technical Abstract

Listeria monocytogenes has been associated with several foods considered to be at low- and moderate risk by published risk assessments, such as celery, lettuce, cantaloupe, and stone fruit. L. monocytogenes is known to be present in low numbers in produce production environments; therefore, it is critical to manage L. monocytogenes risk on intact whole produce along the supply chain. The goals of this project are to determine L. monocytogenes growth and survival conditions for intact whole produce and to develop risk models for selected commodities that demonstrate growth or enhanced survival. We will use a multi-faceted approach that combines industry expertise, previously published data, laboratory experiments, and statistical modeling. The project has these specific objectives:

1. Conduct a systematic review to identify and characterize published data on the growth and survival of L. monocytogenes on intact fruit and vegetable surfaces. 2. Perform L. monocytogenes growth and survival experiments on intact fruit and vegetable commodities at selected conditions to fill missing data gaps. 3. Develop risk models for a sub-set of fruit and vegetable storage or handling conditions shown to display growth or enhanced survival of L. monocytogenes. An industry expert advisory board will identify typical and abusive conditions for intact whole produce commodities. Temperature and relative humidity are known to play critical roles in pathogen growth and survival, so determining parameters that are typically observed for each fruit and vegetable commodity or commodity group is essential. A systematic review of prior literature on growth and survival dynamics of L. monocytogenes on intact fruit and vegetable surfaces does not exist and will be created in this project. Selected L. monocytogenes growth or survival experiments will be performed to fill data gaps based on our systematic literature review. Three types of experiments are envisioned as arising from the systematic literature review: i) where L. monocytogenes data is missing (e.g., L. monocytogenes is an emerging concern in this intact fruit or vegetable and hasn’t been studied) and or ii) where a sub-set of L. monocytogenes data is missing (e.g., L. monocytogenes behavior is unknown at a specific set of storage conditions not investigated by previously published studies) for a fruit or vegetable surface or iii) where the published data show conflicting data (e.g. growth and decline). Experiments performed to fill data gaps (designed experiments in response to the systematic review, Obj. 2), will be used in combination with data from previously published studies (identified in the systematic review, Obj. 1) to develop risk models targeted at commodities or commodity groups sharing similar growth and survival patterns. The identification of intact fruits and vegetables that support the growth and or enhanced survival of L. monocytogenes at specified conditions along the produce supply chain (e.g., typical or abusive storage temperature, relative humidity) will help the produce industry identify commodities or handling conditions where improved handling practices with have the greatest effect on reducing risk.